Civil Engineering Reference
In-Depth Information
Table 3.6 Indicative Number of Heavy Vehicles Expected Per Year and Per Slow Lane
N
obs
Per
year and Per
Slow Lane
Traffic Categories
2.0
10
6
1 Roads and motorways with two or more lanes per direction
with high flow rates of motortrucks
0.5
10
6
2 Roads and motorways with medium flow rates of motortrucks
0.125
10
6
3 Main roads and motorways with low flow rates of motortrucks
0.05
10
6
4
Local roads and motorways with low flow rates of motortrucks
A traffic category on a bridge should be defined according to EC1, for
fatigue verifications, at least, by the number of slow lane and the number
N
obs
of heavy vehicles (maximum gross vehicle weight more than
100 kN), observed or estimated, per year and per slow lane (i.e., a traffic lane
used predominantly by motortrucks). The traffic categories and values may
be defined in the National Annex. Indicative values for
N
obs
are given in
Table 3.6
for a slow lane when using Fatigue Load Models 3 and 4. On each
fast lane (i.e., a traffic lane used predominantly by cars), additionally, 10% of
N
obs
may be taken into account. For the assessment of general action effects
(e.g., in main girders), all fatigue load models should be placed centrally on
the previously defined notional lanes. For the assessment of local action
effects (e.g., in slabs), the models should be centered on notional lanes
assumed to be located anywhere on the carriageway. According to EC1,
fatigue Load Model 1 (similar to LM1) has the configuration of the charac-
teristic Load Model 1, with the values of the axle loads equal to 0.7
Q
ik
and
the values of the uniformly distributed loads equal to 0.3
q
ik
and (unless oth-
erwise specified) 0.3
q
rk
. The load values for Fatigue LoadModel 1 are similar
to those defined for the Frequent Load Model. However, adopting the
Frequent Load Model without adjustment would have been excessively
conservative in comparison with the other models, especially for large
loaded areas. The maximum and minimum stresses should be determined
from the possible load arrangements of the model on the bridge. Fatigue
Load Model 2 consists of a set of idealized motortrucks, called “frequent”
motortrucks, to be used as defined in the succeeding text. Each “frequent
motortruck” is defined by the number of axles and the axle spacing, the fre-
quent load of each axle, the wheel contact areas, and the transverse distance
between wheels (see
Tables 3.7-3.9
). The maximum and minimum stresses
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